Load antenna synchronization table (LSYNC)

RVP10 can operate in a mode where radar data are acquired in synchronization with the antenna motion along the azimuth or elevation axis. This means that the user computer does not need to separately monitor the antenna angles and request each data ray individually.

To use this mode, TAG0-15 must be wired to receive azimuth angles and TAG15-31 must be wired to receive elevation. Angle input may be 16-bit binary angles or 4-digit BCD. This synchronization mode is the only one that ascribes meaning to TAG inputs (usually they are only passed on to the user computer as ancillary information).

Antenna synchronization is done using a table of trigger angles. This table, which contains 3 ... 4096 angles, defines the angle boundaries for each processed ray. The trigger angles do not need to be uniformly spaced nor must they span the full 360° rotation. This gives flexibility in the choice of angles. For example, if local obstructions cause shadows in the radar image, then those regions can be skipped by omitting table entries in their vicinity. Likewise, as the antenna rotates, data can be acquired within one or more sectors by specifying the appropriate sets of contiguous bearings at the desired angular resolution. On power-up, the angle table is initialized to 360 values corresponding to half-integer-valued degrees from 0.5 ... 359.5°.

The synchronization algorithm works automatically with clockwise or counterclockwise antenna rotation, and can tolerate any sequence of changes in direction, for example, if the antenna scans a sector, or turns erratically. The trigger angles do not have to be hit exactly to start each new ray – the antenna only needs to move across them. This minimizes the possibility of losing data due to missing codes in the angle encoders. RVP10 automatically produces an output ray after one second of waiting, even if no trigger angles have been crossed. This prevents time-outs with the host computer when the antenna is not moving.

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|   |   |   |   |   |   |   |   |    |   |   |   |   |   |   |   |
|       |Dyn|Sht|Ena|El |BCD|Ld |            | 1   0   0   0   1 |  Command 
|-------|---|---|---|---|---|---|---|--------|----|--------------|
Dyn

If set, the endpoints of each ray are synchronized. Their angular width can vary by what is required to collect the SOPRM number of pulses.

If clear, the angular width of each ray is fixed (between successive table entries) by adjusting the pulse count and reinterpreting the SOPRM sample size as a maximum value.

Sht

Synchronized rays ordinarily are the full width of successive table entries (in the static case) or the full requested pulse count (dynamic case). This bit modifies the behavior in both modes to allow short rays to be produced, where the pulse count is less than expected due to encountering a feature in the CPI (usually a trigger transition) that would normally result in the entire ray being discarded.

When this bit is set, the user's code must check the pulse count that went into each ray and manually discard those that are too short to contain useful data.

Ena
Enables antenna synchronization.
El
Synchronization is based on TAG1531 (Elevation) inputs. Otherwise, TAG015 (Azimuth) is used.
BCD
Specifies that TAG angle input is in the form of 4-digit Binary Coded Decimal. Otherwise, a 16-bit binary angle is assumed.
Ld

Indicates that a new table size and array of values follow the command.

If Ld = 0, then LSYNC is a one-word command only. Otherwise, the following words are used to load the new table:

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|   |   |   |   |   |   |   |   |    |   |   |   |   |   |   |   |
|         Number of Trigger Angles that Follow (3 – 4096)       |  Input 1 
|----------------------------------------------------------------| 
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 ---------------------------------------------------------------
|   |   |   |   |   |   |   |   |    |   |   |   |   |   |   |   |
|                            (Ignored)                           |  Input 2
|----------------------------------------------------------------| 
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 ---------------------------------------------------------------
|   |   |   |   |   |   |   |   |    |   |   |   |   |   |   |   |
|          First Trigger Angle (16-Bit Binary Angle)             |  Input 3 
|----------------------------------------------------------------| 
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 ---------------------------------------------------------------
|   |   |   |   |   |   |   |   |    |   |   |   |   |   |   |   |
|          Last Trigger Angle (16-Bit Binary Angle)              |  Input 3 
|----------------------------------------------------------------|

You must configure the system to use the synchronization mode.

  1. Use the LSYNC command to load the trigger angle table.
    1. Choose the number of table entries.
    2. Write the required number of words to RVP10.

      Supply the angles clockwise in a strictly increasing order. They must neither reach nor pass 0° by the table's end. The first value may be 0.

      Use binary angle representation, where Bit 15 represents 180°, Bit 14 represents 90°, and so on.

    3. Set the Ld bit command word to indicate that a new table size and set of angles are being loaded.
    4. Set a flag bit to be set if errors are detected when loading the table of angles.

    See Get processor parameters (GPARM).

  2. Enable synchronized operation by setting the Ena command bit. Set or clear, EL and BCD according to your needs.

    These bits may be used independently of reloading the table values. Thus, antenna synchronization may be turned on and off without having to reload the table each time.

    If there are errors when the table was last loaded, the processor ignores the Ena bit and synchronization is forced off.

    Once enabled, PROC commands are issued in the usual manner to acquire and process the radar data. Either the single-cycle or free-run PROC mode may be used. Data collection proceeds as usual, except that the rays are automatically aligned with the trigger angles.

    The angle sync algorithm is dynamic and works as follows:

    1. Each ray begins immediately upon the user's request, or upon completion of the previous ray when in continuous processing mode.
    2. At the start of the ray, RVP10 finds the pair of sync angles that enclose the previous trigger angle.
    3. The current ray then runs until the antenna passes outside of either limit, at which point processing for that ray is terminated.
    4. Once this happens, a new trigger angle is assigned based on which limit was crossed.
  3. In the Sample Size field of the SOPRM command, specify the maximum number of pulses present in each ray during angle syncing .

    This is the number of pulses that used when Dyn=1.

    When Dyn=0, the number of pulses may be less if a trigger angle is crossed before the full pulse count can be accumulated